DESCRIPTION: (Applicant's Abstract) Tuberculosis (TB) is one of the leading worldwide causes of death among adults. The death rate due to TB is, unfortunately, expected to increase due to increasing drug resistance among TB strains and the increase in disease rate among HIV infected and IV-drug using individuals. Consequently, the long-term objective of this research proposal is to improve the understanding of TB pathogenesis so that novel targets and strategies may be discovered to better combat TB. The specific aim of the proposed research is to determine a molecular mechanism involved in reactive nitrogen intermediate (RNI) resistance of M. tuberculosis (Mtb), the etiologic agent of TB. This will be accomplished by 1) comparing the sequence differences between a variety of Mtb clinical, 2) correlating these differences with respect to RNI susceptibility in-vitro, and 3) analyzing the effect on function of site directed protein mutagenesis. In addition, a comparison of macrophage function between iv-drug users vs. non-iv-drug users will be analyzed using a number of iNOS expression assays. This will give support to the hypothesis that chronic injection drug use promotes the selection of Mtb strains resistant to NO due to constant stimulation of the host immune system. This research will provide a better understanding of the molecular mechanism(s) behind NO resistance among various strains of Mtb and furthermore determine of RNI production is in any way modified with respect to chronic drug use.